Upon the continuous casting of flat slabs of steel, proper control of the casting process causes great difficulty. Particularly upon the introduction of the melt through an immersion nozzle which extends into the mold below the bath surface of the casting to be produced, great difficulties in the undisturbed course of the casting process result due to the small distances between immersion nozzle and wall of the mold and the very narrow space available. In particular, there is a danger that the immersion nozzle will come into contact with the solidification front of the shell of the casting and cause damage to it, thus leading to breaks in the casting.
From Swiss Patent No. 619 873, a distributing trough with immersion nozzles and vertical adjustability by means of a lift device is known in which the lift device is program-controlled. The adjustability however serves to fix a given predetermined pouring position of the distributing trough or the immersion nozzle. Furthermore, the plant described there is operated with control of the pouring level. The lift device and adjustment of the pouring level, however, operate independently of each other.
A control device for distributing troughs with immersion nozzles for small billet formats is described in Stahl und Eisen (1988), pages 281 to 285, in which case the casting-on and the displacement in height of the distributing trough during the pouring are included in the control means. The displaceability in height of the distributor is used to control the wear of the immersion nozzle in the slag zone.
From Federal Republic of Germany OS No. 34 23 475 a method of continuous casting is know which uses a controlled starting process and subsequent control of the pouring level. Important parameters of the casting process are controlled or regulated by a casting-shell final thickness calculation in a measurement-value computer. As important parameters it mentions the oscillation of the mold, the amount of flux powder, the quality of the flux powder or also the conicity of the mold.
However, these literature references do not provide any indication of the importance of the distance between the lower edge of the immersion nozzle and the casting shell present in the mold.